After more than 13 years of drug development work, Optimer Pharmaceuticals of San Diego moved into the world of drug sales Monday with the launch of its first commercial product, a prescription antibiotic for treating a potentially deadly intestinal infection.

Dificid was approved by the Food and Drug Administration on May 27 as the first new treatment approved in more than 25 years by regulators for Clostridium difficile.

Optimer said Monday that it launched the drug with its partner Cubist Pharmaceuticals, which has sold its own antibiotic for MRSA and other skin infections in hundreds of hospitals across the country since 2003.

Like MRSA, C. difficile has become rampant among hospital and nursing home patients, especially the elderly.

"We have assembled a world-class, hospital-based product launch team in the U.S. . . . that we believe, when combined with Cubist, will make the Dificid launch one of the most impactful in the hospital segment," said Pedro Lichtinger, president and chief executive officer of Optimer.

Shares of Optimer were down 28 cents, or more than 2 percent, to $11.14 in late morning trading on a day when mounting concern over European debt troubles and stalled negotiations over the U.S. budget debt ceiling pulled down the broader markets.

Optimer is betting that Dificid will quickly emerge as a preferred treatment for C. difficile over vancomycin, the only other government-approved treatment for the infection.

Both drugs knock out the bacterium equally as well, but only 13 percent of Dificid patients redevelop the infection within 25 days of the end of treatment, according to studies conducted by Optimer. After taking vancomycin, the bug resurfaced in 30 percent of patients during that period.

The San Diego company's confidence was reflected in its pricing for Dificid, which costs $2,800 for a 10-day course of tablets. That's double the price of vancomycin, which runs between $1,000 and $1,500 for a full-treatment course.

Dificid could generate more than $123 million in annual sales by 2013, according to stock analysts Thomas Russo with the firm Robert W. Baird in Chicago.